System and method for wide-area stratospheric surveillance

ABSTRACT

Methods and apparatuses for providing wide-area surveillance with a radar and/or other sensors from a stratospheric balloon launched from a land or ship platform for detection, tracking, and classification of maritime, land, and air objects such as ships, people/vehicles, or aircraft are described generally herein. In one or more embodiments, an apparatus is battery operated and includes a stratospheric balloon filled that is filled with helium when it is launched and a gondola with a radar system and communication equipment suspended therefrom. When launched, the apparatus can travel with the wind until it reaches an altitude of approximately 68,500 ft., then it can move substantially horizontally with the stratospheric winds until it returns to earth via a parachute. Multiple apparatus launches at periodic intervals can help provide continuous coverage of the surveillance area. The apparatus can be recovered and re-used or can be considered expendable.

CROSS-REFERENCE TO RELATED PATENT DOCUMENTS

This patent application claims the benefit of priority, under 35 U.S.C.§119(e), to U.S. Provisional Patent Application Ser. No. 61/638,457,titled “SYSTEM AND METHOD FOR WIDE-AREA STRATOSPHERIC SURVEILLANCEPLATFORM,” filed on Apr. 25, 2012, which is incorporated by reference inits entirety.

TECHNICAL FIELD

The patent document pertains generally to radar systems, and moreparticularly, but not by way of limitation, to a system and method forwide-area stratospheric surveillance.

BACKGROUND

Radar systems are used to detect targets in a variety of environments.Coherent radars are often expensive and therefore may be impractical touse on a large scale. Non-coherent radars are cheaper, but may be lessaccurate than coherent radars in some environments.

SUMMARY

In various examples, radars and radar processing discussed herein may beimplemented using methods as described in U.S. Pat. No. 8,330,647,“Sensor Suite and Signal Processing for Border Surveillance” and U.S.patent application Ser. No. 13/317,099, “DETECTION OF LOW OBSERVABLEOBJECTS IN CLUTTER USING NON-COHERENT RADARS,” both of which are herebyincorporated by reference in their entirety.

This document generally describes various embodiments of a low-costWide-Area Stratospheric Surveillance Platform (WASSP). WASSP can includea radar system (e.g., a Smart Sensing Radar System (SSRS)-V200 fromVista Research, Inc. of Arlington, Va.) product implemented in aspecial-purpose launch and recovery package (e.g., a ModularStratospheric Radar Segment (MSRS)) suspended from a stratosphericballoon (e.g., a balloon from Aerostar, Inc. of Sioux Falls, S. Dak.).While camera sensors have been included as part of surveillance systems,radar systems have not been and many would not consider the use ofnon-coherent radars for performance reasons. In an example, a radarsystem is included, because a smart sensor radar processor may makedetection of land, maritime, and/or air targets possible from astratospheric balloon platform. Additionally, the use of a freely movingstratospheric platform or quasi-stationary stratospheric platform with aradar, as described in various examples, has not been tried before. Invarious examples, the power spectrum is computed and processed whenusing a WASSP.

One or more embodiments, can have uses in defense, homeland security,intelligence agency endeavors. For example, WASSP can provide the AirForce with a tactical weather-resistant, high-altitude Intelligence,Surveillance, and Reconnaissance (ISR) capability that can be launchedfrom shipboard or a small land area in a short-period of time, such asless than 30 minutes. The radar system can enable all-weather trackingof low-observable land (e.g., personnel or small vehicles, among otherobjects) and maritime (e.g., small boats or other water craft) targetsto ranges over 100 km radius and greater than 30,000 km² in area.

FIG. 1 illustrates an example of output from a video simulation of thecoverage from WASSP and demonstrates an example of a free-floatingballoon mission using actual wind data from the region. FIGS. 2 and3A/3B illustrate an example of the MSRS with the radar system in bothlaunch and recovery configurations (FIGS. 3A/B) and in surveillanceconfiguration (FIG. 2). The total platform can weigh less than 250 lb.The platform can include an antenna with an aperture of 8.5 ft. thatrotates 360° to provide Wide Area Surveillance (WAS) coverage. In one ormore embodiments, a WASSP includes two Technology Readiness Level (TRL)9 products, a Vista SSRS and an Aerostar stratospheric balloon platform.

WASSP can be a relatively affordable tactical ISR system that isdesigned to be launched, recovered, and re-flown. Because of its lowcost, it can be operated in an expendable mode, such as when used in anarea where recovery may not be practical. WASSP can be launched in lessthan 30 minutes by a 2-person crew. WASSP can move to an altitude of65,000 to 80,000 ft., where it can slowly drift (e.g., with the wind)over the coverage area. At such altitude, WASSP can be difficult todetect. Even if detected, and even if shoot-down were possible, the costto shoot down a platform at these altitudes can exceed the WASSP cost.

The WASSP radar can cover, for example, a 100-km radius (200-km diametercoverage region) and can provide tracking for one or more targets ofinterest within the coverage region for a period of about 8 to 48 hoursover each location with each sortie (e.g., deployment). In embodimentsusing TRL-9 balloon platforms, WASSP can provide a low-risk combinationof technologies for proving the feasibility of radar missions at thesealtitudes. As station-keeping airship technology matures, coverage canbe expected to extend over a location for about a month. By launching aWASSP system every 7 hours from a ship in the Persian Gulf, continuoushigh-resolution coverage of nearly the entire region can be achieved.Each location of interest along the trajectory can have 11 hours ofcontinuous radar surveillance with each deployed WASSP system. Thetrajectory in FIG. 1 shows WASSP payloads landing on command in arecoverable area where the radar units can be picked up and returned forreuse.

The high-performance SSRS Wide-Area Surveillance (WAS) capabilities havebeen validated in extensive Office of the Secretary of Defense (OSD)Assessment Development Group (ADG) tests. The OSD ADG have used WASRadar-Aerostats in Afghanistan Forward Operating Bases (FOBs). Due toits stratospheric ISR capability, WASSP can extend the coverage ofproven 360° SSRS land-maritime radar capabilities to automatically trackand identify low observable (e.g., Radar Cross Section (RCS) less than 1m²) targets of interest, such as dismounted walkers to 65 km range(e.g., greater than 8,000 km²) and small vehicles and boats to over 100km range (e.g., greater than 30,000 km²). Such tracking andidentification can be in oversea conflict areas, and can be accomplishedwithout operator adjustment or interpretation. WASSP can providewide-area Situational Awareness (SA) (e.g., directly) from astratospheric ISR platform to authorized mobile users with a SSRS“Stratospheric IP in the Field” tactical network.

WASSP can be useful in high-terrain conflicted or denied areas wheresensors require high grazing angles for effective ISR or militarycommunications (Comms), and in areas where country-wide and deepcross-border ISR may be desired. This disclosure addresses United StatesAir Force (USAF) critical security areas and Joint Urgent OperationalNeeds (JUON) for wide-area surveillance. OSD ADG test results indicatethe SSRS radar can have a 99% probability of tracking low observableswith a false track rate of less than about one per six hours in diverseweather, land-sea clutter, and terrain.

Warfighter benefits can include improved radar performance and wide-areasituational awareness already proven on Afghanistan SSRS programs.Additional unique WASSP benefits include increased tracking coveragefrom a single location (due to altitude), low purchase and operatingcost, expendability, survivability in conflicted areas, automatedtracking while remaining undetected by targeted objects, and a“Stratospheric IP in the Field” situation awareness network forwide-area support to authorized users during Combat Search And Rescue(CSAR) operations in hostile areas.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which:

FIG. 1 illustrates a simulation of Wide-Area Stratospheric SurveillancePlatform Coverage using actual wind data, according to an example;

FIG. 2 illustrates an overview of a Wide-Area Stratospheric SurveillancePlatform, according to an example;

FIGS. 3A and 3B illustrate an overview of a Modular Stratospheric RadarPackage, according to an example;

FIG. 4 illustrates a vertical profile of atmospheric wind speed as afunction of elevation, according to an example;

FIG. 5 illustrate an analysis of winds over El Paso, according to anexample;

FIG. 6 illustrates an overview of a smart sensor radar system accordingto an example;

FIG. 7 illustrates an antenna azimuth radiation pattern, according to anexample;

FIG. 8 illustrates an elevation pattern of a waveguide antenna,according to an example;

FIG. 9 illustrates computed SNR curves, according to an example;

FIG. 10 illustrates clutter-to-noise curves, according to an example;

FIG. 11 illustrates signal-to-clutter curves, according to an example;

FIG. 12 illustrates antenna gain curves, according to an example;

FIG. 13 illustrates radar tracks of walkers, according to an example;

FIG. 14 illustrates a comparison of radar tracks, according to anexample; and

FIG. 15 illustrates a flow diagram of an example method of detectingtargets using a balloon platform.

DETAILED DESCRIPTION

In various embodiments, a stratospheric, weather-resistant, low-cost,wide-area surveillance system can include a high-performance trackingradar system mounted on a stratospheric balloon platform for situationalawareness of land and maritime targets. A WASSP can address a USAFdesire and a JUON desire for enhanced ISR with a unique, affordable,surveillance capability not presently available to the USAF or any ofthe military services. In various embodiments, the WASSP can include twoTRL 9 Commercial Off-The-Shelf (COTS) systems, an SSRS provided by VistaResearch, Inc., and a stratospheric balloon platform provided byAerostar International, Inc. At a planned mission altitude, the WASSPcan be difficult to detect by the targeted objects. The WASSP can be arelatively low-cost radar system, with relatively low surveillanceoperating costs.

An SSRS can be deployed for wide-area tracking of land, maritime, andair targets, from tower, vehicle, ship, and aerostat platforms. The SSRScan be for wide-area persistent surveillance applications using low-costradar systems. The SSRS radar system can operate from all of theseplatforms without the motion of the platform impacting its performance,and it can take advantage of higher elevation to see targets that arehidden from view at lower elevations. Real-time tracking functions(e.g., algorithms developed by Vista) can use BayesianTrack-Before-Detect processing over a 360° radar field-of-regard toobtain a high probability of detection (>99% for small (RCS<1 m²))and/or slowly moving targets (velocity˜1 m/s) for maritime (e.g.,jet-skis, speedboats, ships, or the like), land (e.g., people, groups ofpeople, small vehicles, or the like), and air (e.g., ultra-lights,Unmanned Aerial Vehicles (UAVs), small aircraft, or the like)applications, and a very low false track rate (e.g., less than one falsetrack per six hours). A more detailed description of the capabilities ofexample SSRS and Smart Sensor Radar Processor (SSRP) systems ispresented in this disclosure as well as in the methods of '647 Patentand '099 Application, which have been incorporated by reference.

As illustrated in FIG. 2, the WASSP system can include two segments. Thefirst segment can be a Stratospheric Balloon Segment (SBS), which can bea TRL-9 COTS 68,000 cubic foot Aerostar product that can bring the radarsystem to an elevation of 65,000 ft. (or higher), and the second can bea MSRS, which is a modular package configured for operation with the SBSat the altitudes and conditions found between 65,000 ft. and 80,000 ft.The MSRS can be suspended from the balloon, and is capable of lifting250 lbs. to the required altitude.

In an embodiment, the protective roll-cage shown at the bottom of FIG.3B is designed to protect the system for recovery during parachutelanding. The MSRS can be designed as a modular system and can includefive assemblies: (1) a command and control assembly; (2) a battery pack;(3) a radar processor (e.g., with data recording for checkout testing);(4) radar electronics; and (5) an antenna or antenna control. A groundstation module can be implemented (e.g., based on a mobile PersistentGround Surveillance System (PGSS) ground station for Unmanned AircraftSystem (UAS) and aerostats) to track the position and coverage area ofthe WASSP over time and to display the tracks of the detected targets ona map of the coverage area.

In various embodiments, the WASSP is an affordable tactical ISR systemthat is designed to be launched, recovered, and re-flown. It can belaunched from the deck of a ship, or from a small truck or trailer, orfrom the land. The WASSP can cover a surveillance region of over 200 kmin diameter from an altitude of 68,500 ft. In part because of its lowcost, it can also be operated in an expendable mode if used in an areawhere recovery may not be practical or possible.

In an example, a land launch can include an Aerostar stratosphericballoon carrying a UAV. A land launch can include enough space to layout the balloon on the ground so that it can be filled with helium andlaunched, such as from a single location. The balloon can have a volumeof about 13,000 ft³ and be designed to carry a 50-lb payload to 65,000ft. In an embodiment, the launch of the balloon takes about 10 minexclusive of any payload checks. This time includes the layout,inflation, and release of the balloon.

In various embodiments, the WASSP can be launched so that once itreaches a surveillance altitude (e.g., about 65,000 to 80,000 ft.), itmoves with the stratospheric winds until it is over or within range ofthe surveillance region.

FIG. 4 shows an example of a vertical profile of wind speed with aminimum in the wind speed found in the stratosphere where flightoperations can be used with the various examples described here. Thevertical profile is of the atmospheric wind speed as a function ofelevation in feet. Note the minimum at 68,500 ft. in the stratosphere.(X: 0-90 kt.; Y: 0-115,000 ft.)

FIG. 5 illustrates a Cumulative Frequency Distribution (CFD) graph forEl Paso, Tex. for the month of October compiled from data collected overa 7-year period from 2001 through 2006 at 50 mb. The plot (X: 0-50 kt.;Y: 0-100%) indicates the percentage of the time that the wind speeds (inknots) are less than or equal to the wind speed on the x-axis with highwinds speeds (e.g., greater than 20 knots) occurring 10 to 20% of thetime. The median (50%) wind speed is 8 to 10 kts. As illustrated thewind speed is <10 kts 51% of the time in October. The actual wind speedson the day of a launch can be known or predicted and the number oflaunches and coverage area can be computed from these wind speeds. At 10knots, the radar can cover an area with a diameter of about 200 km in aperiod of about 11 hours, which means that the coverage of a WASSP atany location along the trajectory of the WASSP is 11 h. For continuouscoverage, like that illustrated for the Persian Gulf in FIG. 1, a WASSPcan be launched about every seven hours. At wind speeds of about 2.5knots, the coverage time can be about 44 hours or about two days. Atwind speeds of about 25 knots, the coverage time is can be less thanfour hours. Wind speeds can be generally lowest during the non-wintermonths (e.g., April-October in the United States) and the wind speedscan increase during the winter months, but winds during the winter arelow enough to allow operation of the WASSP.

FIG. 5 is illustrative of an example of the type of winds anticipated atthe flight altitudes of interest. The figure illustrates that the windspeeds in the proposed stratospheric flight region can be low enough tosuccessfully operate the system. The actual wind velocities, of course,depend on location and season, and can be different depending on the dayor time of operation. In an embodiment the coverage area and the time onstation is dependent on the atmospheric wind speeds at altitude and thecapability of the radar. Aerostar has accumulated a library ofstratospheric wind speeds at 50 and 70 mbar and compiled CFDs as afunction of location and month/season like the one shown in FIG. 5. Upto one or more days of coverage with one or more WASSPs can be possible.The surveillance range can be over 200 km and the surveillance time cantypically range between about eight hours to two days.

In various embodiments, the command and control assembly includes aGlobal Positioning System (GPS) module, a Federal AviationAdministration (FAA) transponder control, primary flight terminationsystem, backup flight termination system, discrete relay control forexternal payloads, analog voltage readings from external payloads, andexternal RS-232 (or other communication protocol) payload commandinterface. Telemetry data can be passed to the ground station by a 900MHz line-of-sight link. For tests conducted with the real-time radar, aclient display can be used to display and interact with the targettracks generated by WASSP. Many different communication links can beused, such as a long-range (500 nm) OTH link.

Power budget calculations were made for the WASSP system that indicatethat a single 55 lb. battery can be sufficient for WASSP operations ofabout 24 hours or less. Calculations can be made to determine whether ornot solar power should be added to the system. In an example, thebattery can be flown on balloon flights at altitudes above 130,000 ft.

The efficiency of a battery at the temperature conditions found ataltitude can be about 50%. The excess heat generated from the radarsystem can be directed to the battery assembly via a heat pipe to heatthe battery assembly and increase its efficiency. This implementationcan have one or more advantages including removing excess heat from thesystem or increasing the life of the battery.

The SSRP shown in FIG. 6 can be used to acquire, digitize, or otherwiseprocess data from the WASSP. Target tracks, target information, andrelevant environmental and control data can be transmitted via awireless data link to a ground control station for use on a clientdisplay. The client display can be used in maritime and land radarapplications. For radar tests, the radar data can be recorded on disk(e.g., solid state disk drives), such as for post-test analyses. TheSSRP processor can be sealed and conduction cooled. This can be donethrough heat conduction to the battery, where the heat can be used tokeep the battery warm and increase the efficiency of the battery. Theradar data recorder can be based upon the S902R sealed computer fromGeneral Microsystems Inc. of Bellevue, Wash. The MS S902R is a fullysealed and rugged computer with a solid-state drive array.

In various embodiments, the SSRP shown in FIG. 6 is a specially packagedsupercomputer that digitizes raw video I and Q output from the radarreceiver and processes it using one or more algorithms (e.g.,proprietary algorithms). In various embodiments, the algorithmimplementation can use existing tracking algorithms that areincorporated in the SSRP. For example, real-time detection and trackingalgorithms can include full Bayesian track-before-detect processing fora 360° radar field-of-regard, which can be executed in the SSRP. TheSSRP system can be hosted in a rugged box, such as a 4 U (7 in.) high by21 in. deep box based on a military qualified system. In an embodiment,a Remote Control Unit (RCU), also shown, can allow the radar to beoperated at remote locations, such as can be used in tower, building,aerostat, and mobile vehicle platforms. When the radar already existsand provides appropriate information to the SSRP, such as already existsin most ships with TARS, the RCU may not be needed. The SSRP trackingsystem can develop and maintain track on many thousands of targets inthe surveillance region. In various embodiments, both the RCU and SSRPcome in indoor and outdoor mechanical packaging. The SSRP can be offeredas two distinct products, one for maritime applications and one for landtargets. The distinct products include a Land Radar Processor (LRP) fordetection and tracking of people, vehicles, and low-flying aircraft, anda Maritime Radar Processor (MRP) for detection and tracking of smallcraft, boats, ships, and low-flying aircraft.

In various embodiments, the performance specifications for SPRS systemsdelivered to oversea areas have been rigorously tested and proven at USGovernment integration sites and controlled FOB test ranges (test siteslocated in Arizona, Colorado, and North Carolina) by several assignedindependent test agents for the Government (including APL). ControlledFOB protection tests and operator training can be conducted by theGovernment with SSRS in oversea-like environments, including desertsummer conditions, high altitude, and complex terrain. SSRS systems canmeet MIL-STD-901 and MIL-STD-167 standards requirements. Data streamscan use sockets (e.g., TCP/IP) to expose data in a continuous mannerwithout requiring requests from the end user. An SSRP can be capable ofstreaming data in a number of formats including, but not limited to,eXtensible Markup Language (XML), National Marine ElectronicsAssociation (NMEA), or binary, among others. To utilize a data stream auser can know the SSRP host name or IP address and/or the TransmissionControl Protocol/Internet Protocol (TCP/IP) port that the data isexposed on. Multiple data streams can allow multiple simultaneous clientconnections in accordance with a system Interface Control Document(ICD). In various embodiments, the SSRP can be integrated with over 10different coherent and non-coherent radars.

In an embodiment the power consumption of the S902R is less than 50 Wand the weight of the S902R is less than 2.5 lb. The S902R can bepackaged in a rugged sealed enclosure with the Radar Control Unit, whichcan include a digitizer card, timing signals and provide thermalcoupling to the battery. The data to be recorded can be rawIn-phase/Quadrature (I/Q) data from the coherent radar receiver, whichcan implement 500:1 pulse compression. These inputs can digitized in16-bit samples, for example, and at a rate sufficient to meet thebandwidth requirements. Processing can be done digitally in the SSRPprocessor. The data can be Doppler processed and then entered into aBayesian track-before-detect radar processor (e.g., a radar processorfrom Vista). Tracks can be mapped into ground coordinates andtransmitted over a wireless link by the real time processor. In sometests (e.g., initial tests), the data can be simply stored and processedon the ground.

In various embodiments, there are several alternatives to the recorderconfiguration, including using the Mercury SBC3510 Single Board Computeror the 6 U module LDS6521. These single-CPU modules are availableconduction cooled and rated to 68,500 ft., with the caveat that it isthe responsibility of the user to keep the conduction-cooled card edgesat 71° C. The cards have a Switched Mezzanine Card/Peripheral ComponentInterconnect (PCI) Mezzanine Card (XMC/PMC) mezzanine site for thedigitizer card, which can be the dual-channel Mercury Echotech ECV4-2PMC card. The cards can be mounted in a sealed and conduction cooledenclosure such as the Dawn VPX 3 U conduction cooled enclosure for UAVapplications.

For the fully integrated and deployed system, most or all of theprocessing can be done on the WASSP MSRS. In one or more embodiments,the data may not be recorded. In such embodiments, only the outputtracks may be provided to the client display on the ground station, suchas can be similar to the other SSRP and SSRS applications. The radarprocessor can run on Intel® Central Processing Unit (CPU) hardware, butother hardware may be used. These modules can be checked to verify theycan operate under the deployed conditions. Heating of the processor orchanging some of the internal modules may be used in testing.

In various embodiments, the WASSP radar is a modified Kelvin Hughesradar unit, which has a 200 W peak power, fully coherent pulse-Dopplersystem with high pulse compression capabilities. The WASSP can includethe waveform generation, RF transmitter and receiver components, and IFcomponents to produce baseband I and Q channel signals, and radar PulseRepetition Frequency (PRF) timing signals for the processor and datarecording use. In an embodiment, the radar assembly accepts the antennaposition encoder signal from the antenna controller and can supply thissignal to the processor.

In an embodiment, the Radar Electronics Assembly (REA) is packaged in amodular box and can provide heat transfer from the transmitter poweramplifier to the power assembly, such as to dissipate heat from thepower amplifier. This heat transfer can be done via a heat pipesubassembly, because normal convection cooling may not be effective atsome operational altitudes. This assembly can include a Kelvin Hughestransceiver along with the necessary power conditioning and signaltransfer electronics needed. The coupling to the antenna can be througha WR-90 waveguide, for example.

The Kelvin Hughes system can be normally used in marine radarapplications with the antenna scanning controlled by another assemblysupplied with that radar system. For the WASSP, in an embodiment, theKelvin Hughes antenna scanner can be replaced by a Vista antenna andantenna control assembly.

A special antenna can used in WASSP. The antenna beam can be narrow inboth azimuth and elevation. Both the antenna position relative themodular assembly and the rotation rate of the antenna can be controlledto obtain accuracy in target location estimation.

In an embodiment, the antenna is designed to provide a one-way halfpower beam width of about 0.75° in azimuth and about 6.4° in elevationgiving a directivity of about 39.3 dBi. The antenna can include aplurality of waveguides (e.g., fourteen) stacked vertically with theface of the antenna tilted down, such as by about 15 degrees, from thehorizon. The antenna polarization can be approximately horizontal and a9.41 GHz power can be split into channels to feed each of thewaveguides. In an example including 14 waveguides, the power can besplit into 14 channels. The losses of the splitter, waveguides, andconnections can be about 2.2 dB, so the net antenna gain can be about37.1 dBi. FIG. 3A shows the front of the waveguide antenna assembly,according to an example embodiment.

In various embodiments, the azimuth pattern is achieved by using astandard WR90 aluminum waveguide (e.g., about 0.400″×0.900″ insidedimensions with 0.050″ walls). In an example, slots can be cut in itsnarrow wall and the slots can be slightly tilted to achieve a desireddistribution over the length of the guide. Each waveguide can be end-fedthrough a waveguide 2-way splitter and an output from one of two stripline 7-way dividers.

In an embodiment, the far end of the waveguide is terminated (e.g.,grounded) to prevent the small amount of energy remaining to not bereflected back toward the source. The slots can be spaced so that thephase of the radiation from them is proper to form a beam approximatelyperpendicular (broadside) to the length of the waveguide. The amount ofradiation by each slot can be a function of the tilt from vertical ofthe slot. The radiated amplitude distribution across the length of thewaveguide can be a Taylor 25 dB distribution, such as to give low sidelobes in a reasonably efficient aperture. Such a configuration canprovide a beam peak that is squinted about 5° from broadside in thedirection of the terminated end of the waveguide. The squint angle canchange with frequency at a rate of about 0.008 degree per MHz. Invarious embodiments, the antenna design is a non-resonant array topermit operation over a 300 MHz bandwidth. The antenna design can becentered at about 9.41 GHz. In an embodiment, the slots can be spacedabout 0.996 in. apart, and 100 slots can be used to give a radiatingaperture of about 100 in. (8.25 ft.). The one-way half-power beam-widthcan be about 0.75 degrees and the two-way half-power beam-width can beabout 0.54 degrees. An example of a one-way azimuth radiation pattern isshown in FIG. 7.

In various embodiments, the elevation configuration can be an array of14 radiators, as described above, about equally spaced vertically andall fed in phase to form a beam perpendicular to the surface. Theelevation pattern of a single waveguide can be broad. A narrow elevationpattern of about 6.4 degrees can be obtained from 14 waveguides spacedabout 0.93 inches apart. The power can be split to provide a modifiedcosine amplitude distribution across the vertical aperture, so as toprovide about 23 dB sidelobes. The one-way half power beam width can beabout 6.38 degrees and the two-way half power beam width can be about4.56 degrees. An example of an elevation pattern of a waveguide antennais shown in FIG. 8.

The power handling capability of a WR90 can be conservatively rated atabout 200,000 W at sea level and at about 15° C. At an altitude of about68,500 ft. and at about −55° C., this degrades to about 7,000 W. Thus,there can be a considerable safety margin for the transmitter power ofthis radar.

In various embodiments, the antenna controller includes an antennarotation motor, a closed-loop motor controller, position encoder,position encoder signal conditioning circuit, and a DC-DC-converter. Amotor control subassembly can provide the mounting position for theantenna support and rotator shaft. FIGS. 3A and 3B illustrate an exampleof an antenna controller between a radar assembly and an antenna.

In an embodiment, the rotation motor can be a direct-drive DC motor,such as a direct-drive DC motor with a maximum torque of about 2.8ft-lbs. Such a motor can bring the antenna rotation up to its speed of 1RPM in approximately 30 s. A maximum of about 5 W can be used during thestartup interval. After the antenna is rotating at speed, the speed canbe maintained within about 0.05%, and the position reporting accuracycan be about the same. With the signal conditioner power requirementsand the DC-DC converter efficiency, this unit can operate nominally atabout 10 W total, at least two different voltages (e.g., 12 VDC and 5VDC).

In various embodiments, the radar assembly houses a modified KelvinHughes radar system. The radar assembly can be located above the antennacontroller assembly. The radar unit and the antenna can be interfacedvia a WR90 waveguide from the radar transceiver to the antenna feedguide through an access hole between the two boxes. Screws (e.g., flangescrews) for this connection can be accessible from one side of each box.The radar assembly can include a DC-DC converter, such as to conditionthe battery power to the limits needed by the Kelvin Hughes radar unit.This converter can be controlled via a relay from the Processor/Recorderassembly. The radar can nominally consume about 200-210 W at about 18-33VDC.

In various embodiments, a Radio Frequency (RF) power amplifier in theradar unit can perform better if some heat is dissipated therefrom.Since convection cooling may not be readily available at about 65,000 toabout 68,500 feet altitude, the radar unit can be mounted on a heat pipeevaporator element, such that the heat can be transferred upward to thepower assembly, where the condenser for the heat pipe can be in contactwith the battery pack. Such a configuration can have the effect of usingthe batteries as heat sinks for the power generated by the radarfrequency power amplifier.

In an embodiment, the antenna is suspended below the electronics modulesand can scan at a rate of about 1 RPM, for example. The rotatingelements can be configured to be balanced and can include the ability toadd weight as required. FIG. 3A shows an example of the antenna andlower payload assembly.

The antenna can be made of three functional sections: (a) the activearray, including slotted waveguide elements; (b) the support frame; and(c) a structure to support and to position the array elements. Thesupport frame can attach the whole to the rotator shaft and theelectronics modules.

The active array can include parallel aluminum waveguides (e.g., 14parallel waveguides). In one or more embodiments each waveguide can beabout 8.5-ft. long and spaced at intervals of about 0.93 in. Thewaveguides can be machined in a precise rigid fixture and restrained inthe antenna support structure in the same rigid position. The waveguidescan be precisely located on the frame and held rigidly in parallelpositions.

In various embodiments, the support frame is a bolted and brazedassembly. The support frame can carry the power splitters, and a feedwaveguide that connects the radar to the antenna and provides attachmentto the rest of the system. The rotating shaft can be attached to aboutthe center of the top beam of the support frame. In an embodiment thatincludes a radome, the radome can be made of about 0.06-in. FiberglassReinforced Panels (FRP) and can add about 45 lbs. to the system weight.

In various embodiments, the rotating mass can weigh about 61 lbs. andcan have a moment of inertia of about 130 lb. in s². An angular momentumfrom a configuration of 1 RPM may not include rotational stabilization.Stabilization is possible and can include adding a counter rotating mass(e.g., a flywheel) between the motor and the antenna. A second motor canbe used with electronic rather than mechanical gearing to help stabilizethe system.

In an embodiment, an electronics module contains the direct drive motor,feedback encoder, power supply, and motor controller. The motor can bemounted to a lower bulkhead, and the drive shaft can be bolted directlyto the motor. The motor can have a through hole configured to allow thepassage of a WR90 flanged waveguide and provide a direct path for thewaveguide to the antenna. The lower bulkhead of the module can bereinforced so as to help bear the load of the rotating antenna assembly.

The antenna can be connected to the modified Kelvin Hughes radar via aWR90 waveguide through a rotary joint that can be located within thehollow drive shaft. The shaft can be a gasket sealed around the rotaryjoint on the lower side.

In various embodiments, the electronic modules are about 24 in² with theheight adjusted to fit the contents of the given module. The bottom trayof the antenna controller can be strengthened to carry the suspendedrotating mass.

The general characteristics of the radar system for operation from astratospheric balloon can be application specific. The radar can operatefrom an altitude of about 68,500 ft. This, together with power andweight constraints, may create a high-grazing angle, thus making theclutter return from the ground or sea significant. De-cluttering can beaccomplished, such as by using Doppler processing. In configurationsthat include Doppler processing, a dwell time on the order of 100 ms.can be implemented. Such a dwell time can affect the rotation rate. Therotation rate is inversely related to the beam width. The Signal toNoise Ratio (SNR) and the range accessible to the radar with acceptableSNR can be a function of the antenna gain and radar power.

Two performance criteria are modeled using the parameters in Table 1-1:

(1) the SNR, which is the radar return from a target with a given crosssection versus the system noise, and (2) the Signal-to-Clutter Ratio(SNC), which is the radar return from a target with a given radar crosssection versus the radar background clutter.

TABLE 1-1 Frequency: 9.41 GHz Pulse width: 240 ns (compressed) Power:100 kW (compressed) PRF: 1200 Hz Antenna RPM 1 Noise figure: 6 dBLosses: 4.6 dB Lookdown angle: 15° Target RCS: 10 m{circumflex over( )}2

There can be adequate SNR to operate the radar beyond ranges of about100 km radius (e.g., a coverage of about 200 km diameter). Second, theSNC can allow tracking of small, moving targets using Dopplerprocessing.

Using the selected Kelvin Hughes X-band radar, the performance model wasrun for antenna and other system parameters. Estimates of SNR are shownfor a target of about a 10-dB cross section in a maritime environmentwith sea state 3. The radar used has about a 200-W amplifier and about a500:1 pulse compression, is horizontally polarized, and has a maximumduty cycle of about 13%. This radar is outfitted with a suitablehigh-gain antenna, and the antenna is pointed down toward the surface,such as at an optimal angle.

In various embodiments, the Doppler spectrum of the return from the seasurface is expected to be similar to that shown in the example of FIG.9. The Doppler spectrum of the clutter return can depend upon sea stateand wind direction, but in general it can be expected that the returnfor this type of radar (with a large resolution cell) can have a roughlyGaussian spectrum with about a 3-dB width less than about 1 m/s centeredat a velocity of order about 1 m/s. The clutter return from the sea, inthe Doppler domain, can be contained within a few meters per second.This means that Doppler processing can enable the detection of targetswith velocities outside this band and against the thermal noise of theradar. The clutter and noise return from land can be similarly limitedto a band around zero velocity—the mean at about zero. The width of theclutter spectrum can comes from the internal motion of vegetation on theland. The clutter spectrum can be exponential in shape and containedwithin about ±1 m/s, as observed in radar tracking of individual peoplewalking at about this velocity, edging up against the clutter spectrum.The statistical distributions of the fluctuating amplitude from bothland and sea clutter have also been studied in detail and are can havelong tails, so that the Doppler processing and separation in the Dopplerdomain may be used for success in detection with radar. A maritime radara with high rotation rate, such that it gets only a few pulses on agiven target, may not succeed when deployed to a proposed elevation.These radars are usually employed at low altitudes, with small grazingangles, because the clutter decreases for these smaller grazing angles.

In various embodiments, the grazing angle for a stratospheric radar atabout 68,500 ft. ranges from about 45 degrees at about 22 km in radiumto about 12 degrees at 100 km in radius, and may not reach the smallgrazing angle regime. The SNR for a single dwell with this radar with anantenna measuring about 10 ft. by about 15 in., with a horizontalbeamwidth of about 0.75 degrees in azimuth and about 6.4 degrees inelevation, tilted down about 15 degrees, is shown in FIG. 9. The rightpanel shows the SNR as a line plot for several selected radar heights,as indicated in the legend at the upper right. The model shown in FIG. 9includes the effect of multipath interference, which can enhance ordegrade the performance at small grazing angles. At the large grazingangles that are obtained in this example (e.g., about 12 to 45 degrees),multipath may not play a role.

The antenna gain was computed in a similar way as the SNR shown in FIG.9 and is shown in FIG. 12. This computation shows that a lobed nature ofthe SNR can be due to a narrow vertical beamwidth of the antenna. Thiscan provide an antenna gain of about 37.4 dBi. As previously stated, theantenna can be pointed downward at about 15 degrees from horizontal. Thebeamwidths can be one-way 3 dB (half power point) widths of theradiation pattern. The antenna pattern was computed with a cylindricalwave front at the aperture having a departure from flat phase of about1.2116 wavelengths and cosine amplitude weighting across an aperture ofabout 12 wavelengths. This produces a pattern with a smooth fall-offangle. Since the SNR is a function of the square of the gain, a highgain of an antenna can be helpful.

With respect to FIG. 12, the figures were obtained with the parametersin Table 1-1, which were estimated for this application. From theseparameters the effective number of pulses in a dwell is about 107, andthe SNR shown reflects the coherent integration of this number ofpulses, thus providing a gain equal to about the number of pulses. Thetarget was presumed not to fluctuate during the dwell. Theclutter-to-noise ratio is shown in FIG. 10 and the signal to clutterratio in FIG. 11. These figures illustrate that coherent Dopplerprocessing to separate the target from this fluctuating clutter returncan be helpful.

The following provides an Overview of Vista's Smart Sensor Radar System(SSRP) and Smart Sensor Radar Processor (SSRP) for Maritime and LandRadar Processors. In various embodiments, a comprehensive line of SmartSensor Radar Processor (SSRP) products for maritime, land, and aircraftwide-area surveillance applications using low-cost COTS radar systemsand a SSRP processor are used in the above system. The algorithmimplementation in this effort can be performed using existing trackingalgorithms that are incorporated in the SSRP. Real-time detection andtracking algorithms, which includes full Bayesian Track-Before-Detectprocessing for a 360° radar field-of-regard, can be executed in theSSRP. In an embodiment, the SSRP system, which is hosted in a ruggedbox, 4 U (7 in.) high by 21 in. deep and based on a military qualifiedsystem, is shown in FIG. 6. A Remote Control Unit (RCU), also shown, canallow the Radar to be operated at remote locations and is used fortower, building, aerostat, and mobile vehicle platforms. When the radaralready exists and provides appropriate information to the SSRP (such aswith most ships and the TARS), the RCU may not be needed. In anembodiment, the SSRP tracking system is able to develop and maintaintrack on many thousands of targets in the surveillance region (see FIG.13). Both the RCU and SSRP come in indoor and outdoor mechanicalpackaging.

These products can be operated from a ship, a tower, a truck, abuilding, or an aerostat, or other locations. While there are manydifferences in these platforms and their impact on the performance of aradar system, two examples include elevation of the radar relative tothe elevation of the target; and motion of the platform. In general,higher elevations provide better target visibility to the radar, andthus small targets, which may be hidden from terrain or man-madefeatures on land or waves in the maritime environment, may be observedat higher elevations. Each of the platforms can move and this movementcan affect the performance of the radar system. The SSRP can operatefrom all of these platforms without the motion impacting itsperformance. The SSRP can take advantage of the platforms with higherelevations to see targets that are hidden from view if the radar ispositioned too low. Low elevations for radars located on mobileplatforms can be about 20 to 30 ft. off the ground and high elevationsfor radars can be on aerostats that are at about 300 ft. to greater thanabout 10,000 ft. Ship masts and towers range in height from 40 ft. to100 ft., with many towers being 60 to 100 ft. Buildings can provide awide range of elevations. To achieve the best performance, radars shouldoperate at low grazing angles and understand the impact of multipath,both of which are a function of radar elevation. This processing systemsof the present disclosure have been successfully used at large grazingangles when deployed for aerostats at elevations ranging from 500 ft. toover 10,000 ft.

The SSRP can operate with low-cost, COTS, X-band, noncoherent maritimenavigation radars, but the SSRP can also be used with both noncoherentand coherent Doppler radars over a wide range of radar frequencies(e.g., X-, Ku-, C-, S-, and L-bands). The MRP and LRP can detect targetswith small radar cross-sections (RCS<1 m²) for maritime (i.e., anythingthat is on the surface of the water from jet-skis to speedboats to largeships), on land (i.e., people, groups of people, and small vehicles),and in the air (i.e., ultra-lights and small aircraft) applications.High performance has been achieved because of the implementation ofspecial signal processing algorithms developed to address the detectionand tracking of small targets at long ranges with very low false alarmrates as discussed in the '647 Patent and '099 Application. In variousembodiments, the SSRP achieves a probability of detection of >99% ontargets with cross sections of 1 m² and a false alarm rate of less than1 false target every six hours. Illustrations of this capability arepresented in FIGS. 13 and 14.

In various embodiments, MRP algorithms can achieve a high level ofperformance against small targets, because they allow operation in highclutter conditions produced by adverse weather (rain), high winds, andhigh sea states where other systems fail. Thus, small targets can bereliably detected at longer ranges than normally possible without falsealarms overcoming the system. MRP has demonstrated the capability todetect and track small targets moving across frozen lakes likesnowmobiles and small, slow-flying aircraft. For identification andclassification purposes, Advanced Imaging Solution (AIS) information canbe automatically correlated and superimposed on the MRP detections andtracks. The situational awareness developed from MRP detections andtracks can provide important information and alerts about potentialthreat situations. The MRP and LRP have been used with X-band andS-bands maritime radars, but can be used with other types of radarsystem, including Doppler radars. For example, the MRP was installed onthe existing L-band Doppler radar on the TARS (at elevations of about10,000 ft.) in Lajas, Puerto Rico, for assessing improvements fortracking small maritime surface vessels at ranges up to 200 nm.

In various embodiments, LRP algorithms can achieve high performanceagainst small, slow moving targets like people and small vehicle,because they can operate in high clutter conditions produced by movingtrees and vegetation during windy conditions. As part of the evaluationtesting, the SSRS system was operated from a 90-ft tower and from alow-altitude aerostat. The SSRS outperformed the other radars mounted onthe tower by a factor of 10, and the SSRS was the only radar system thatcould be operated from the aerostat. Controlled targets with GPSconsisted of people walking and vehicles. FIGS. 6 and 13 illustrate theSSRP 25 kW Radar System deployed from a 90 ft. tower at the Yuma ProvingGrounds (YPG). FIG. 13 shows results from this system and illustratesthat the LRP can detect and track small land targets like walkers out toranges greater than 10 km, and these detections and tracks are notmasked by false alarms. The Vista SSRS mounted on the aerostat canperform about equally as well as the Vista SSRS mounted on the tower forboth walkers and vehicles. Single walkers can be detected and trackedout to about 11 km in this configuration, and small groups of walkers (2to 3) were detected and tracked out to about 18 km in thisconfiguration. Vehicles and other objects with larger radar crosssections than people were detected and tracked out to distances of about25 km. The SSRS on the aerostat extended the range to over 40 km,because terrain features, which can obstruct visibility from the towerdid not obstruct visibility from the aerostat.

In an example, while testing at YPG, vehicles at ranges of about 28 and34 km were tracked using a SSRS on the aerostat. During the tests atYPG, measurements were also made from an aerostat positioned atelevations ranging from about 500 ft. to about 2,000 ft. In someinstances, the aerostat and tower LRP measurements were madesimultaneous from the same ground location. Similar results for bothpeople and vehicle targets were routinely observed from both platforms.The results indicated that vehicles can be detected at greater rangesfrom an aerostat than from a tower. This can be because of the higherelevation of the aerostat (e.g., 2,000 ft. compared to 90 ft.).

FIG. 14 illustrates an application for the SSRP where only a subset ofthe processor was used to reduce the false alarms of border surveillanceradar systems operated from a 25 ft. mast on a stationary vehicle. Inthis case, only the detection outputs of the radar were processedcompared to applications where the SSRP starts its processing on the rawdata. FIG. 14 shows the impact of wind when it blows bushes before(left) and after (right) the application of the SSRP processor. Thetargets identified in green on the right panel processed with the SSRPare not discernible on the left panel processed with the radar itself. Auser in such a situation can have to choose between tracking all or noneof the targets on the left because there may be too many targets totrack. An advantage of the SSRP can include the capability for operatingat a very low false alarm rate. This is also true of the SSRP when usedfor maritime applications.

The SSRP (LRP) has been extensively evaluated for performance during awide range of realistic operational conditions, including adverseweather and high clutter conditions, by Department of Human Services(DHS) on the Southern Border of the United States, in the SouthernCalifornia desert areas by the Army Night Vision Laboratory (NVL), andon numerous occasions at YPG by OSD, U.S. Navy Naval Air Systems Command(NAVAIR), and the Army. After competitive evaluations, the SSRP radarsystem was selected and is presently being implemented on towers andaerostats for deployment to Afghanistan. Vista's SSRP radar system wasthe only radar system to operate successfully on both the towers and theaerostats, and was the only radar system tested that would operate froman aerostat. Tower motion impacted the performance of Vista'scompetitors, and there was no competition for radar measurements fromthe lower-elevation aerostats.

The SSRP (MRP) has successfully undergone extensive and thorough at-seaevaluations and extended operational tests under a wide range of wave,wind, temperature, and weather conditions for and funded by the US Navy,the Canadian Border Patrol (CBP)/DHS (on Lake St. Clair), and a majorcommercial shipping line (in the Atlantic Ocean, the Mediterranean Sea,and the Gulfs along the East African Coast (Somalia)). The MRP candetect, track, and provide situational awareness alerts for maritime andaircraft applications, including targets traveling on ice. The Navycompared the MRP to other trackers over a range of weather and waveconditions. They found that the MRP outperformed the competition by afactor of 2 to 10 in terms of detection performance, range ofdetections, target size, and weather conditions. In various embodiments,the MRP outperforms the competition in terms of false alarm rejection bya factor of about 10. DHS has also reviewed multiple systems and chosethe MRP for the Detroit area. The MRP has been operated in winds up to35 knots or greater during rain, other adverse weather conditions, andin sea states that exceed sea state 5. The U.S. Navy has successfullyevaluated the MRP installed on a Navy combatant ship deployed to themiddle east. The DHS and CBP have been successfully operating and usingthe MRP installed on a tower on Lake St. Clair for border surveillancesince last winter and is in the process of installing a second one tocomplete coverage of the border in the lake.

The MRP was also evaluated on two 40-day cruises on a large ocean-goingship. The MRP was retrofitted to the X-band and S-band radars already onthe ship. The results confirmed results from the U.S. Navy tests andwent further—the MRP encountered and successfully operated in a widerrange of adverse weather and higher sea state conditions (over Sea State5).

The SSRP-MRP was also deployed on the USAF TARS aerostat in Puerto Ricoto help expand the capabilities of TARS beyond solely tracking of largeair targets, for maritime tracking of small/slower surface targets bymultiple U.S. Government agencies in the Caribbean. The MRP tracks canbe generated onboard the TARS aerostat for small-large maritime targetsat ranges of up to 400 km from the aerostat site, and then transmittedto a server (e.g., a real-time server). In this example the real-timeserver was located in Arlington, Va. These tracks can be provided asnear real-time tracking services over internet (TCP/IP) networks tomultiple operational users along the east coast including CAMOC (SanJuan), USCG (San Juan), Naval Research Lab, and USCG Miami, such as byusing a reachback server.

The MRP has operated on the Lajas TARS. Sea surface and air targets canbe tracked by the MRP. There is an AIS feed in this configuration, sosome of the tracks can be displayed with SSRS radar data. This same feedcan support graphic association of Blue Force data with SSRS tracks.This configuration can allow a user to determine (e.g., quicklydetermine) if a track is due to a known vessel, or an unknown. Thiscapability supports effective observation, identification, andapprehension of unknown targets. If other track information, such asBlue Force/Identification Friend or Foe (IFF), are available, then thosecan be displayed in the same manner. For the TARS, if radar contacts outof the native TARS processor are available, then those contacts can bedisplayed.

In various embodiments, the SSRS-MRP has been deployed remotely on acoastal tower on Gull Island to monitor maritime traffic on Lake St.Clair with the radar track results being sent to the OperationalIntegration Center (OIC) at Selfridge. A second SSRS-MRP system is beingdeployed at Grosse Point. Prior to deployment, the SSRS-MRP radar wassuccessfully demonstrated in cold (sub-freezing), rainy, and windyconditions in December 2009 from a short (25-ft) scissor-lift on LakeSt. Clair. During these tests the SSRS-MRP operated in subfreezingconditions “24-7” for six days. In this time the SSRS-MRP detected andtracked controlled targets (e.g., jet skis, 18 and 25-ft boats) equippedwith GPS. Additionally, low-flying aircraft/helicopters and channelmarkers were tracked. Winds of 15-20 knots, rain, snow, 20°-40° F.temperatures, and waves over 3 ft. on a 20-mile lake that is about 20-ftdeep were encountered during this testing period. The SSRS-MRP radarsystem effectively detected and tracked all of the targets, and insubsequent tests, demonstrated that SSRS-MRP can effectively tracksnowmobiles after the lake freezes.

An extensive set of at-sea tests were conducted using control targets(e.g., jet skis, Zodiacs, 7-m and 11-m Rigid-Hulled Inflatable Boats(RHIBs), and larger craft). The analyses showed that SSRS-MRPoutperforms other systems in terms of probability of detection, targetsize, range, false alarm rejection, and operation in adverse weather andwave conditions.

In sum, the SSRS-MRP has over 10× lower false track rate than othercompetitors; over 10× better detection performance than SPS radars(operated with operator assistance) currently used on U.S. Navy and U.S.Coast Guard ships; effectively operates in adverse weather conditions(rain), while other radar systems produced unacceptably large numbers offalse alarms due to rain; operates in wave conditions higher than SeaState 3, while other systems are limited to much lower sea states; andcan be fully automatic while other systems require operator tuning andoperator expertise to run the radar and to interpret the results.

Both the ocean-going ship and the CBP/DHS Lake St. Clair tests confirmedand extended the test results obtained in the at-sea Navy evaluation,except the wind, wave, and weather conditions were larger and moreadverse.

The SSRP client display can include functionality to allow an individualuser to tailor usage to his/her requirements without altering otherusers' views. Functions are designed to help with situational awareness.In various embodiments, some features include: (1) Replay to allow auser to review tracks in the past (e.g., 9 weeks), such as at speedsfaster than real time, so as to help find out where a target came fromor look for patterns; (2) Bookmark to allow a user to save (e.g.,quickly) a time for later replay; (3) Track Annotation to allow a userto change a threat level, such as by using Naval Tactical Display System(NTDS) and MIL-STD-2525 symbols, or name a target—note: these actionscan then be seen in the displays of other users; (4) Track history andCourse leaders to allow a user to quickly see where the target has beenand where it is predicted to go, note that a user can adjust how many ofthese are visible; (5) Hook tracks to allow a user to mark a track andsee its key information on a side window for quick reference; (6) Filtertracks to allow a user to Dim or remove tracks from an individual user'sdisplay based on speed, distance from the radar and other similarfilters. This does not necessarily affect the tracks viewed by otherusers—it can display tracks differently to aid situational awareness,such as for a user only looking for a small speed range of targets; (7)Distant Measurement to allow a user to determine distances between twopoints on the screen; (8) Screen Markings/Drawings to allow a user tocreate shapes on the display to aid situational awareness by markingareas to look for targets in or other uses; (9) Map backgrounds to allowa user to switch the background (e.g., available on the system oravailable on a LAN) of the displayed screen; (10) Zoom and pan to allowa user to view a region as large or small or change the colors of tracksas desired; (11) Turn a track source on or off to allow MRP tracks, AIS,IFF, and other radar detections or tracks to be displayed (e.g., all atonce).

FIG. 15 a flow diagram of an example method of detecting targets using aballoon platform. In various examples, a method for detecting land,maritime, or air targets may include using a radar system mounted on afreely floating stratospheric balloon platform. The platform can moveover the radar surveillance area. In an example, the platform movesusing the stratospheric winds. In an example, the platform includespropulsion means (e.g., propeller fans etc.) to remain approximatelystationary over a radar surveillance area.

In various examples, a radar system may be mounted in a gondolierstructure (e.g., a gondola, FIGS. 2, 3A, and 3B) suspended from aballoon platform. The gondolier structure can include a battery powersupply system, an antenna system, a command and control system, and aradar data collection and processing system. The antenna can beprotected by a structural enclosure (e.g., roll cage) during launch andrecovery of the gondolier structure. In an example, the structuralenclosure can open during radar surveillance to allow the antenna torotate for data collect. The antenna can rotate 360 degrees at a setrotation rate. The rotation rate can be set or changed by a command andcontrol system on the gondolier structure (e.g., automatically or byreceiving instructions from a ground operator). In an example, thecommand and control system includes navigation means (e.g., GPS sensor,transponder) for locating the position of the balloon platform. Invarious examples, the balloon platform can include communication means(e.g., receiver, transmitter, transceiver) to communicate with thesurface (e.g., an operator or control system) to receive instructionsand provide output from the radar system or other sensors on the balloonplatform. The communication means may include a high frequency system.

In various examples, the radar system on the balloon platform is anon-coherent radar system. Radar data from the radar can be processedafter computing the power spectrum of the radar data. In an example, theradar system is a coherent radar system.

In various examples, the balloon platform is launched from a land,maritime, or air platform. The balloon platform can move into thestratosphere, collect radar data and other surveillance data, and returnto the surface of the earth. In an example, the balloon platform isexpendable. In an example, radar processing software, radar data, andprocessed results can be destroyed (e.g., a timeout or by receiving aninstruction from the ground) if the platform is not recovered or isconsidered expendable. In an example, the balloon platform isrecoverable and reusable.

In an example, the balloon platform includes a data acquisition andprocessing system. In an example, the processing system is a smartsensor processing system. Sensors may include an imaging sensor such asan EO/IR camera system. In an example, data obtained from the radarsystem other sensor systems may be combined in a data fusion (e.g.,overlaying data received from the radar and other sensors in a display).

Although various examples, has been described with reference to specificexample embodiments, it will be evident that various modifications andchanges may be made to these embodiments without departing from thebroader spirit and scope of the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense. The accompanying drawings that form a parthereof, show by way of illustration, and not of limitation, specificembodiments in which the subject matter may be practiced. Theembodiments illustrated are described in sufficient detail to enablethose skilled in the art to practice the teachings disclosed herein.Other embodiments may be utilized and derived therefrom, such thatstructural and logical substitutions and changes may be made withoutdeparting from the scope of this disclosure. This Detailed Description,therefore, is not to be taken in a limiting sense, and the scope ofvarious embodiments is defined only by the appended claims, along withthe full range of equivalents to which such claims are entitled. As itcommon, the terms “a” and “an” may refer to one or more unless otherwiseindicated.

What is claimed is:
 1. A method comprising: launching a surveillanceplatform, the surveillance platform including: a stratospheric balloon;a gondolier structure comprising a battery power supply system, anantenna system, and a command and control system, wherein the gondolierstructure is suspended from the stratospheric balloon, and wherein theantenna system is protected by a structural enclosure during launch andrecovery of the gondolier structure; and a radar system, wherein theradar system is mounted in the gondolier structure; and opening thestructural enclosure of the antenna system during radar surveillance toallow the antenna to rotate for data collection; setting the rotationrate of the antenna to rotate 360 degrees; detecting land, maritime, orair targets in a radar surveillance area with the radar system; andtransmitting, from the surveillance platform, data associated with thetargets detected by the radar system.
 2. The method of claim 1, furthercomprising incorporating propulsion means on the surveillance platformand using the propulsion means to have the surveillance platform remainapproximately stationary over the radar surveillance area.
 3. The methodof claim 1, wherein setting the rotation rate includes setting therotation rate using the command and control.
 4. The method of claim 1,wherein the command and control system includes a GPS.
 5. The method ofclaim 1, wherein transmitting from the surveillance platform includestransmitting using a high frequency system.
 6. The method of claim 1,wherein the radar system is a non-coherent radar system.
 7. The methodof claim 6, further comprising: computing a power spectrum from radardata collected using the radar system; and after computing the powerspectrum, processing the radar data.
 8. The method of claim 1, whereinthe radar system is a coherent radar system.
 9. The method of claim 1,further comprising: collecting sensor data from a camera on thesurveillance platform.
 10. A surveillance platform to detect and,maritime, or air targets in a radar surveillance area, the surveillanceplatform comprising: a stratospheric balloon; a gondolier structure,wherein the gondolier structure is suspended from the stratosphericballoon and wherein the gondolier structure includes: a non-coherentradar system, wherein the radar system is mounted to the gondolierstructure, and wherein the radar system is configured to compute thepower spectrum of radar data collected by the radar system; a batterypower supply system; an antenna system; a structural enclosureprotecting the antenna system configure to open during radarsurveillance, wherein the structural enclosure is a roll cage; and acommand and control system.
 11. The surveillance platform of claim 10,wherein the command and control system includes a GPS.
 12. Thesurveillance platform of claim 10, further comprising propulsion means.13. The surveillance platform of claim 12, wherein the propulsion meansallows the surveillance platform to remain approximately stationary overthe radar surveillance area.
 14. The surveillance platform of claim 10further comprising communication means to communicate data collected bythe radar system.
 15. The surveillance platform of claim 10, wherein theantenna includes an active array including slotted waveguide elements, asupport frame, and a structure to support and to position the arrayelements.